fetch latest nimby release (#4501)

- `0.1.6` appears to have been removed, latest is `0.1.13`
- let's change it to always fetch the latest to ensure we get a release
that exists

Author: monofuel

.github/actions/setup-environment/action.yml

@@ -54,7 +54,7 @@ runs:
     - name: Set up nim
       shell: bash
       run: |
-        curl -L -o nimby https://github.com/treeform/nimby/releases/download/0.1.6/nimby-Linux-X64
+        curl -L -o nimby https://github.com/treeform/nimby/releases/latest/download/nimby-Linux-X64
         chmod +x nimby
         ./nimby use 2.2.6
         echo "$HOME/.nimby/nim/bin" >> "$GITHUB_PATH"